To understand the mechanism(s) responsible for toxicity of xenobiotics capable of forming fatty acid (FA) conjugates, the investigators characterized rat liver FA ethyl ester synthetase (FAEES) isozymes that conjugate xenobiotics to FAs. The studies indicate that pancreatic and plasma FAEES are structurally and functionally different from those they characterized in the liver. Therefore, in Aim 1, they will purify and characterize FAEES from pancreas and plasma and establish their interrelationships to each other and to the liver enzymes by comparing structural and functional properties. These relationships will be further characterized using inhibitors (e.g., tri-o-tolyphosphate) and inducers (e.g., phenobarbital) of FAESS. In Aim 2, the relative formation of FA conjugates will be examined in hepatoma cell lines expressing different levels of enzymes involved in the conventional oxidative metabolism of the model compounds methanol and aniline. In Aim 3, the formation, kinetics and enzymology of FA conjugation of biologically important functional compounds will be investigated in vivo and in vitro and in cell culture. Finally, in Aim 4, the mechanism of toxicity of FA conjugates of methanol (FA methyl esters) and aniline (fatty acid anilides) will be evaluated in vivo. The mechanism by which FA methyl esters inhibit Kupffer cell function (phagocytosis) will be thoroughly investigated by studying their metabolism and effect on energy production. Similarly, the pancreatic toxicity of FA methyl esters will be evaluated, along with the evaluation of FA anilides to induce autoimmunity, and associate mechanisms. The project may provide a clear understanding of the formation of FA conjugates of xenobiotics, the enzymes involved in this process and the mechanism(s) by which such conjugates exert their toxicity. This information may be important in devising approaches to prevent the toxicities mediated by FA conjugates.